1. Field of the Invention
The present invention relates to a thermal head and a thermal printer, and more particularly to a thermal head and a thermal printer using a single crystalline silicon substrate.
2. Description of the Related Art
In recent years, thermal heads for performing thermosensitive recording by selective heat generation of a heat generating element have been used.
Japanese Patent Application Laid-Open No. H02-137943 discloses a thermal head using a single crystalline silicon substrate.
The thermal head disclosed in Japanese Patent Application Laid-Open No. H02-137943 includes: a heat generating element formed on a single crystalline silicon substrate via an insulating film; a driver circuit unit formed on the single crystalline silicon substrate; a wiring layer for connecting the driver circuit unit to the heat generating element; and a protecting film for protecting a thermal head surface.
The protecting film contacts a printing medium such as an ink sheet and thus requires abrasion resistance, and is formed of a hard insulating layer of SiO2, Si3N4, SiON or Ta2O5 having a thickness of several μm.
The insulating film used as the protecting film in Japanese Patent Application Laid-Open No. H02-137943 has a small thermal conductivity, and for example, SiO2 has a thermal conductivity of 0.9 W/m·K, and Si3N4 has a thermal conductivity of 16 W/m·K.
The insulating film has the large thickness of several μm for providing abrasion resistance, and thus it takes a long time for heat generated by the heat generating element to transfer to the printing medium to increase a printing time.
An insulating film between the heat generating element and the silicon substrate has an equal thermal conductivity to that of the protecting film, but has a thickness of around 1 μm smaller than that of the protecting film.
Further, the silicon substrate has a large thermal conductivity of 152 W/m·K, and thus thermal energy generated by the heat generating element easily escapes toward a heat sink to cause a large loss of the thermal energy.
The present invention has an object to reduce a thickness of a protecting film having a small thermal conductivity.